"My primary concern is the ability of the two to set aside their pro-union advocacy past and act as neutral arbiters between employees and employers, so those parties can trust them to fairly adjudicate labor disputes," Alexander said. "Will they be judges and not advocates? So far, my concerns haven't been lessened.

The confirmation vote was 13-9. Republicans have complained the five-member board hasn't been impartial enough in dealing with disputes between employers and unions.